Can a constructor be a virtual method?

No.

Virtual functions are used to ensure polymorphism through late binding, where the specific version of the function is called at runtime depending on the actual type of the object.

The constructor is responsible for initializing an object of a specific type during creation. Since the type of the object is known at runtime within the constructor, there is no need for polymorphic constructor selection. A virtual call does not make sense in the context of object creation.

Additionally, the vptr (pointer to the virtual function table) is set within the constructor body after the base classes are initialized. Attempting to call a virtual function inside the constructor will invoke the version from the class whose constructor is currently executing, not from the final derived class. This behavior is incompatible with the idea of a virtual constructor.